Re: Why does not rgrep use "grep -r"?

[Eli Zaretskii <eliz@gnu.org>]

> From: David Kastrup <dak@gnu.org>
> Cc: Miles Bader <miles@gnu.org>,  schwab@suse.de,  lennart.borgman@gmail.com,  emacs-devel@gnu.org
> Date: Sat, 03 Nov 2007 10:43:03 +0100
> 
> Totally warm cache:
> 
> dak@lola:/usr/local/texlive/2007$ time find -name \*.tex|xargs grep snort
> ./texmf-dist/source/latex/ae/aesample.tex:and whooping and sneezing and snorting, that I could not hear myself think for
> 
> real    0m0.974s
> user    0m0.372s
> sys     0m0.536s
> dak@lola:/usr/local/texlive/2007$ time grep -r  --include=\*.tex snort .
> ./texmf-dist/source/latex/ae/aesample.tex:and whooping and sneezing and snorting, that I could not hear myself think for
> 
> real    0m1.225s
> user    0m0.376s
> sys     0m0.764s
> [...]
> On a warm cache, it is pretty much the same.

Perhaps for the Linux filesystem, it is.  It looks as it's quite
different on Windows:

With warm cache:

timep grep -r snort d:/gnu/gdb-CVS/src/gdb > nul

real    00h00m03.171s
user    00h00m00.234s
sys     00h00m02.312s

timep find d:/gnu/gdb-CVS/src/gdb -name "*.c" | xargs grep snort > nul

real    00h00m03.921s
user    00h00m00.015s
sys     00h00m00.015s

That's a 20% difference in elapsed time (the fact that user and sys
are zero is just an artefact of the timep command implementation on
Windows).

With cold cache:

timep grep -r snort d:/gnu/gdb-CVS/src/gdb > nul

real    00h00m15.531s
user    00h00m00.328s
sys     00h00m03.140s

timep find d:/gnu/gdb-CVS/src/gdb -name "*.c" | xargs grep snort > nul

real    00h00m13.687s
user    00h00m00.015s
sys     00h00m00.078s

That's 11%, a much smaller gain, and in the other direction.